mtbvfr

Hi Folks,

This is the first time I am considering doing something like this. I've read through some of the pertinent threads.

I'm looking for some advice regarding Rigid Fork selection to replace the current 100mm Suspension Fork for Touring purposes using a Lowrider rack.

I have been using the free version of BikeCAD but it doesn't recalculate the Head Angle for a change in the Axle to Crown (A-C) and Rake (Offset) for a Fork. However, a previous thread, in this forum, suggests that a change in A-C of 10mm effects a change of 0.5°. I also noticed that the BB Height wasn't being recalculated neither.

The Frame parameters I used are the following for the 100mm Suspension fork at rest.

BB Height: 295mm
Chain Stay Length: 425mm
Effective Top Tube: 594mm

So, for the Fork Parameters I unchecked Suspension and then I altered the A-C (AC) and Rake (R) values and the Head Angle values and Seat Angle values accordingly. For the Wheel, I chose Standard 26 x 2.125/2.2" and then selected Custom and changed the Width to 53mm. The tyre diameter of 670mm appears to be a very close match to the Conti Race King 2.2" that I have inflated to 20PSI with the following results.


Current Fork - 100mm Suspension - At rest
Steerer: 265mm
AC: 480mm, R: 38mm, Head Angle: 71°, Seat Angle: 73°
Calculated Trail: 75mm


Current Fork - 100mm Suspension - allowing for 25mm Sag
AC: 455mm, R: 38mm
Head Angle: 72.25° (BikeCAD used 72.3°), Seat Angle: 74.25° (BikeCAD 74.3°)
Calculated Trail: 67mm


Salsa CroMoto Grande 29er 80mm Suspension Corrected
AC: 468mm, R: 45mm
Head Angle: 71.6°, Seat Angle: 73.6°
Calculated Trail: 64mm
Need a Rack to Suit


Salsa Firestarter
AC: 483mm, R: 45mm
Head Angle: 70.85° (BikeCAD used 70.9°), Seat Angle: 72.85° (BikeCAD used 72.9°)
Calculated Trail: 69mm
This fork would raise the BB slightly. I can't say how much exactly, maybe a 1mm ?, because BikeCAD didn't recalculate this value when changing the Angles and Fork parameters.


Surly Krampus
AC: 483mm, R: 47mm, Head Angle: 70.85° (BikeCAD used 70.9°), Seat Angle: 72.85°
Calculated Trail: 67mm
Ditto for the BB height.

I like that the Salsas have stainless steel fork dropouts.


The Firestarter offers the most Trail. Could/Should I cut the Steerer Tube down to 240mm or 245mm to allow for most of the Sag that would occur for the Suspension fork? I have a 5° stem that can be flipped to make the handlebar higher if I feel the need to.

I'm looking for the bike to be as stable as possible as I'm still recovering from a Dislocated Shoulder and wish to reduce any risk of a fall due to an unstable bike. So, I am hoping those of you with MUCH more experience in bike geometry, both technical and seat of the pants, than me could recommend the most stable option.

Of course, my preferred solution would be to have made a custom Lowrider rack that could be mounted to V-brake bosses and use either P-clamps at the bottom of a Suspension fork, where there is a "ledge" at the front where the fork leg morphs into the Dropout Plate, or the integrated Eyelet of a Rigid fork so that I could use the rack on either my suspension fork or the rigid fork of my old 26" Mountain Bike which also has rack mounts in the middle of the fork legs. Because the external widths of the forks are different, the supporting Arch that loops over the top of the wheel would need to be adjustable for width. Instead of a Curved arch, the Arch would have to be made flat to allow one tube to slide within another to allow a small bolt to be inserted through both tubes and secured by a nyloc nut. Anybody here that can do that?

Thanks, MTB.

Andrew R Stewart 

Don't confuse trail, as the main or sole factor, with stability. The general thought that relates to trail is that the slower you go the more that low trail is right and the faster you go the more higher trail is a benefit. But most trail discussion have it ranging from as low a 30ish mm to maybe as much as 70ish mm. It seems to me that the bike you have is what I would consider a "NORBA racing geometry with a sprung fork". Not what I would first choose for a touring conversion that required a lowering of the front end. Also you talk about BB height when builders generally deal with BB drop. Have you tried to approach the design changes from that reference yet? Have you tried to ride your bike with your fork at 50% or 75% sag yet to see how that was?

Have you checked out the Old Man Mountain specializes in Racks designed to work on all bikes. racks? They can attach via axle and brake posts and have years of reputation behind them. Will you be loading mostly rear or front? This can be a design factor for front end geometry. Generally the more fork biased the load is the shorter the trail is thought to be better.

Don't get too much invested in a few mms of dimensional differences or a couple of tenths of a degree of angle. Do be concerned about your fit. Remember that as the seat angle pivots forward the seat needs to set back, on the post, to retain the original set back WRT the BB. (But who knows if you even have a best fit yet...) This essentially stretches out the reach to the bars, so stem lengths often get shortened. Which changes the feel of the steering. See how circular this stuff can get? At some point one just has to try something and find out in real life with a true load how the bike feels. (Which I asked about riding the current set up with a bottomed out or significantly sagged fork). Andy

fietsbob

Big sheets of paper.. draw it out..



My touring bike (one off) We built a twin plate fork crown 1" steerer and Round fork blades an offset in the crown, so less in the fork blade tip..
It worked..

Try several on your list,

Maybe just buy an imported suspension corrected fork, see if it's Adequate ? add braze ons ...







...

mtbvfr

Hi Andy,

Thanks for the feedback.

You are probably "spot on" with the NORBA reference. The bike is a 2005 Haro V4 18".

I know it's not the best option for Touring but I think it's the best I have to work with for now until I can get out of here and to a place where I can talk with a builder regarding a Custom MTB with a Lower BB that can also be used for Touring.

I started a weight reduction program for this bike because I think it can be lighter than my old 1990 DB Ascent MTB which I used to tour Western Europe and Spain in 1992 with a Lowrider rack for the Front Panniers and I had a Backpack strapped across the of the Rear Panniers and Rack.

Almost every component has been replaced with something lighter. I've already built a new Front wheel and the Rear is still to be started. With the new wheels alone, there will be a weight loss of over 2 lbs with the Rims and Nipples losing 200+g which will help with acceleration and climbing.

I mentioned BB Height because that was the dimension listed on the Haro catalogue. I measured the BB Drop according to the page on the BikeCAD website and it's about 19.05mm .

https://www.bikecad.ca/bb_drop

Don't know when I will get a chance to try your suggestion of increasing the Sag. I just updated the corresponding parameters (A-C, Head Angle, Seat Angle) for 50% and 75% Sag and the Trail for 50% was 60mm and 52mm for 75%.

I know about the OMM racks but they mount on the QR. I've looked at the Zefal Raider Front rack too but that's not a good option because the lower mounting uses a Hose style Clamp and the External Fork diameter reduces in the direction of the axle so the clamp would not fully grip the fork leg and so most of the weight would be hanging from the Brake Bosses.

I was originally thinking I could fit everything on the back with 2 Panniers totalling 40L and a Bag across the Top but after a dry run with the Bag that will go across the Top and being nervous about my shoulder and knowing that I have other things to load on when I get to my initial destination, I've decided it would be prudent to get some weight up front.

So, if the shorter trail would be offset by the use of Low Mounted panniers up front, then, the Salsa CroMoto Grande 29er could be the best option if I could find a way to securely mount a rack to it.

Regarding fit, before I had the accident I was thinking that I needed to be more stretched out. The latest stem 130mm 5° (flipped upside down) and seatpost with 25mm offset will help a bit but of course I haven't been able to test it. I have also changed from a 25° Backsweep Bar to an SQlabs Bar with 35° Backsweep and again haven't been able to test it. I think I need a bike with a longer Top Tube (TT) really. Previously I had been going in the opposite direction with shorter and raised stems on my old DB but I was still sliding forward on the saddle and pushing my butt backwards. The current fork has a 265mm Steerer and I have the Stem at the top of that and the Top of the Saddle is about 30mm below the Top of the Steerer with the Saddle set to the back with about 5mm more to go if needed. However, I have a feeling that this is not the optimal setup for the most ergonomic and efficient relationship between my Hips, Knees, Cranks and BB etc. Hence my comment about maybe needing a bike with a Longer TT. I have long femurs for my leg length but the Left leg is 8mm shorter than the Right with 5mm of that being in the Femur because of a Knee injury when I was 18 and hence the Right leg grew longer and developed a significant pronation due to me favouring the Left leg for 2-3 years. About 10 years back I changed from 175mm cranks to 177.5mm Left and 180mm Right which helped but replacing the 177.5 with a 175mm has been better. I have 177.5mm Right cranks and I would like to be able to get matching 172.5 Left cranks because I think I would be able to spin better. With the setup described above my knee is behind the pedal axle. I can't remember exactly what it was now but it was more than 10mm.

Thanks, MTB.

unterhausen

cut down the steerer tube meaning the bottom of the head tube? I wouldn't do it.

I think you probably wouldn't really notice much difference between those forks, but the ones with too much a/c might have a little too much flop for your tastes. I tend to notice that the most while climbing standing up. Hard to tell without doing it, I think.

I certainly wouldn't make a decision based on stainless dropouts.

base2 

My money is on the Firestarter. IMO it would ride closest to the existing fork. Like was said, a mm or 2 or a .002 of headtube geometry really isn't going to be noticable.

You said you like stable. My mountain bike, a hard tail of 1997 vintage, has a 67 (65? I don't remember...) Head tube angle and 100mm of trail at rest. It's an absolute dog traveling from place to place, but rides like a champ in the down hill single tracks. I would call that way too much for your purposes. Not a joy on the road, at all. It feels like you really need to muscle it around unless you are already standing on the pedals. Just establishing an absolute upper limit, here for demonstration purposes.

My roadbike has a 69.5 head tube angle and 86mm of trail. I went to a straight seat post with zero off-set and a 120mm stem (from 80mm) to move the weight forward. It's super stable, but quick directional changes to miss a pothole or other hazard require a bit of planning. On high speed down hills (40mph plus) it rides amazing. Throw a bend or 2 in that highspeed run though... as soon as it decides you are in a turn, it really decides you are in a turn. I've seriously had soiled chamois concerns a couple of times. I would never place a rack or additional load on the front. Establishing a cautionary tale. You probably don't want anything this stable, other properties emerge.

Any of the forks you mentioned would be fine enough for your uses, except the 29'er canti. The brakes won't line up with your 26 inch rim. I like the Firestarter. Maybe the Krampus if you intend to follow through with the front loading.

base2 

Another thought: If you are replacing the fork anyway, now would be a great time to consider an upgrade to disc brakes.
It would mean a new front wheel, of course. But if your rim is already worn & due for replacement from the rim brakes any way...is it really so much of a cost?

Also, the 2.2 inch tires may be a dog on the road. A skinnier tire would make for a lower trail number & easier rolling than a mtb knobby. Probably what you want here for front mounted rack & longer travels. Continental makes 26 inch Gatorskin road slicks that are 28's or 32's iirc.

Just throwin' it out there.

Andrew R Stewart 

Re tire widths- I run 26 x 1.5 (Panaracer Passella Tourgards) on my touring bike with very good balance between pace, handling, load capacity. My geometry was set with this tire size in mind. 71* head angle with 64mm trail (43mm rake). Andy

mtbvfr

Hi Bob,

No time for Big sheets of paper etc.

A Straight Crown or a Crown angled towards the rear is a good idea I had already thought about to be able to have curved blades so that the bike can plane but I don't want to invest a lot more money in this bike.

Planing
https://janheine.wordpress.com/2018/...es-are-faster/

https://janheine.wordpress.com/2014/...at-is-planing/

https://janheine.wordpress.com/2017/...e-steel-bikes/

What are these imported suspension corrected forks that you are referring to?

Thanks, MTB.

mtbvfr

Hi unterhausen,

No, from the TOP of the Steerer tube, you know, that thing that goes through the Head Tube.

Regarding Wheel Flop, can you describe what it is that you notice the most while climbing standing up?

Thanks, MTB.

mtbvfr

Hi base2,

I can kind of identify with your Road Bike experience. I once had a Road Bike with 73/74 angles, I think, that was a bit nervous at High Speeds, like 80+ km/hr, but I could carve up the corners on fast sinuous descents.

I prefer the CroMoto Grande 29er or the Firestarter over the Krampus because not only are the Dropouts Stainless but they appear to be Thicker too. The Firestarter also has mid-leg Rack mounts.

I already have Disc Brakes which are TRP Spykes and KCNC rotors are going on the new wheels.

The Conti Race King's roll really fast actually on all terrain. They are a Race tyre designed for Hard/Smooth conditions but seem to roll really well on the pavement too. I have a pair of the 2.0" Supersonic version I am saving for special rides. However, I'm going to get 26″ x 1.8″ Naches Pass TC tyres in the Extralight Casing which will reduce rotating weight significantly too and I have some Maxxis 75g tubes to go along with those.

https://www.renehersecycles.com/shop...8-naches-pass/

Thanks, MTB.

Andrew R Stewart 

Really??? Not that I put much merit in the whole discussion surrounding "planning" I do know it's nearly always referenced to frames with an amount of flexibility in the frame. An amount that is greater then typical. Yet here you A) are planning to tour with some weight. This is not where you want a rather flexible frame, especially when you have placed stability on the list. And B) The frame you have is not what I would call a particularly light weight or flexy one. Mountain bike frames with their large diameter tubes tend to be stiff for their size.

Sorry to sound like this but I feel you are focusing on what you want to believe in and not what will be. Andy

duanedr 

High trail, front load and high BB is destined to be such an odd combination of stable and un-stable that I would avoid it.

Have you thought of looking for a suitable used bike on craigslist? Around here, you can get a decent 80's or 90's bike with rack and fenders for around $200 which is probably what you'll spend on a fork and tires. Just a thought - and you can sell it when you are done touring.
Touring
MTB - not suspension geometry

unterhausen

this bike is never going to plane