pressed001

That't about how I feel about it too.

This is also what I have decided. Will stick with 559.

And the wheelbase is 1079mm. Yeah, we'll see how it goes.

Happy Feet

I echo the "try something different" sentiment.

I don't get too excited reading about what people buy. It's like watching the home shopping network. I do like seeing what people build.

Moisture

This bike is most at home on gravel and fast singletrack though

Ironfish653

90's XC bikes are aggro as F.
'NORBA' Geometry was typically 71* / 73* what's so slack about that?

It seems like BF doesn't know that there was a couple of decades between the Schwinn High Sierra and long-travel 29'ers.

Ironfish653

If by 'aggressive' do you mean 'head down, all-or nothing speed merchant' than your '26er in 700c high heels' would work, i guess, but it'd be a lot of weird compromises and workarounds just to have a polished frame.

OTOH, if agressive means cut-and-thrust, around-and-over-anything-in-my-way; then stay on the 559s but don't limit yourself to cheap, skinny 32mm slicks. Conti's Speed Contact 26" comes in 1.6" and 2.0", (42 / 50mm) or BMX 'Park' tires like the Kenda Kinniption and Maxxis DTH, even more volume(2.0"-2.3"), and a little bit of tread, so jumping curbs and taking to the dirt is still on the menu.

Korina

Or split the difference and go with a 650b Surly Midnight Special. Disc brakes, aggressive (whatever that means) all road bike. Not sure why you want to make a mustang into a thoroughbred, but ride your ride.

pressed001

We are indeed a minority.

You should see what I do on my rigids!
According to the '95 GT catalog, the Zaskar (and most likely also my Tempest) have a 70.5° HA which aint too shabby. I would love to increase this with perhaps a 26" front and 28" rear, but the ST° would go from an already steep 73.5° to a ridiculous 76.25°. The slightly shorter than stock 390mm disc fork which I will be using will increase both HT and ST° by 0.25°, putting the bike at 73.75°ST and 70.75°HT.

Love it! This is going to be great. Thanks for the pointers.

I took a good, long look at Surly products and especially their forks. If it wasn't for the ultra-classic look of their forks, probably would have purchased one. They have by far the biggest steel fork collection to be found by any one manufacturer.
------------------------------------

Thanks a lot for the pointers guys. I'm now considering the BB height as the primary driver regarding wheel size.

GT says the BB height is 298. How does this compare with modern road bikes? My cranks are 170mm, so I expect that to help slightly if the BB height is "low", especially with the slicks instead of normal mountain tires. If the BB height will be too low with slicks and 26" rims, I could build some 650's. This is something I need to look into.

ofajen

I would always be considering the specific size of wheel and tire that the frame was designed for, particularly as it relates to the total distance from the front axle to the ground. The head tube angle and fork rake will be designed for a specific total front wheel radius and resulting amount of trail. If you change the total front wheel radius, you will change the amount of trail and that will generally not be an improvement.

Otto

pressed001

So the more I dig into this, the more interesting and exciting it gets.

My GT Tempest:
BB height (manufacturer's spec): 298mm
BB height with 559 rims and 1.35" slicks: 282.3mm
BB height with my 28" road rims/tires: 310mm
BB drop: 32.2mm (calculated based on 26" (660.4mm) rim+tire combination and manufacturers given BB height. This should be checked.)
Front-to-center: 654.7mm
Wheelbase: 1079mm

For comparison:
Scott Scale 925 29" hardtail:
BB height: 312mm
BB drop: 58mm
Front-to-center: 707mm
Wheelbase: 1128mm

Scott Adict RC road bike:
BB height: 274.5mm
BB drop: 70mm
Front-to-center: 588mm
Wheelbase: 992mm

So basically if I build this bike with 28" road rims and tires, the BB will be as high as a typical 29" MTB and if I build it with 26" rims and slicks it will still be slightly higher than the modern road bike. However, my calculations were for fully inflated and unloaded 35mm tires. Loaded and inflated to only 60psi, this BB height should drop to around 277.3 which is spot-on for road bikes!

After reading this great article including comments, I understand more about bike frame geometry and the dynamics of BB height, drop, front-to-center and wheelbase.

At this point I don't believe that BB height alone will have a great impact on handling, but rather BB drop plays here a greater roll especially regarding braking. There's nothing I can do about that though. So what I will concentrate on is keeping the BB height about the same as a typical road bike which means 26" rims.

Also considering the relatively shallow BB drop and braking performance, I think it would be cool to try a dropper post for the downhill portions, letting me get the CoG real low even compared to any road bike, thus letting me corner and brake much more effectively.

pressed001

That's a really good point and yet another thing which I need to read up on; fork trail and handling. Thanks.

pressed001

Put the Kojaks on my wife's SLRs and they seal up and measure a decent width for the rim. Hoping they'll expand out to 35 on the new wheels once I get them built. Was pretty happy how they sealed up with the NoTubes sealant. There was no leaking in the sidewalls, just around the bead initially. They've now been sitting around at max pressure for a week without leaks. The bead was super easy to get on these rims. Hoping that will not be the case with the hookless rims. If correct, it should be a real tight fit.







Happy Easter from our family to yours and God bless.

Moisture

The BB drop on my Zaskars measures to be about 285mm with 26x2" tires fitted. This is low for a XC bike.

The angles are also pretty aggressive. I'd say it's designed more like a flat bar gravel bike.

i took mine out for a quick spin last night. I don't ride mine anymore because its a bit small for me. The bike seems to respond to your inputs particularly well and corners notably faster at lower speeds than my 700c equipped road bike. Its a very fast paced and enjoyable ride.

I've ridden this bike on 26x1.75 tires before (they measured at 1.5" wide when mounted) and, i would never do that again. I would not use anything but 26x2 on this bike as the frame was designed for. It's mostly a factor of staying within the diameter wheel this bike was designed for. I think it can handle some serious singletrack while being very fast on its rigid for if you use thick cushy tires. This does seem to impact response on pavement when pushing hard into turns, but worth the tradeoff. If the bottom bracket was a bit higher I wouldn't hesitate to slap on some long crank arms and thrash this thing on the trails again.

trying out different wheel sizes front and rear like you've suggested is a bad idea. Small deviations in size can be fine, but trying to mess around with angles by using radically different tire or wheel sizes isn't going to work well at all.

I suggest you stick to the tire size this bike was designed for and enjoy it on a variety of different surfaces as the bike was intended for. It's a very fast and stable ride over rougher terrain and fast tight single track.

More fork rake = less trail. Steeper head fune angle also = less trail. When equipped with a standard fork with a standard amount of rake (which will lower the front end and steepen the angles considerably when compared to a suspension fork), you will get a medium amount of trail which is really quite aggressive compared to modern XC bikes. Its a halfway step to road cycling just like a gravel bike.

Last thing I must add, is that when the original owner of my zaskar built it up, he used a 100mm fork which this geometry of frame is not designed for at all. The fork ended up being severely bent as a result. I would not use any suspension fork on this frame, even if it was 60 or 80mm as designed.

Moisture

The zaskar has a long reach more biased toward single track use

70sSanO

I ride 90’s mtb’s. My Serotta is spec’d at 72* head angle, it was 40” WB. But for a road bike, especially wanting one that is aggressive, 70.5* is really slack.

The comparison between my 73* and 74* Cannondales is night and day. My SR400 was kind of a slug compared to my Criterium. I can’t imagine trying to dive into corners with that GT geometry and WB.

John

Wildwood 

Nice family. The girls want their Daddy safe.

You relented on wheels than were not designed for the frame - I suggest you do the same on welding a disc tab on the fork.

Sometimes good advice is good advice for a good reason.

pressed001

Agree. Based on the geometry, it's not a good idea to be playing with different wheel sizes. Also agree, no suspension forks for this frame again because of the geometry. Just not made for it.

The tires can always be exchanged. If the 35mm road tires don't work out, can always revert back to 2". That's kind of what I like about this build. It's very compliant and I can throw just about anything on there to suit my mood.

The reach would be long. Compared the geometry to my other road bikes and will use a 60mm stem to get it perfect for the drop bars (stack also considered and perfect).

Yeah. Will be slack for a road bike. However will be comparable to other gravel bikes with a HTA of about 71°.

Yep. Didn't want to purchase another fork but did it considering safety. Could have welded tabs onto stock GT fork and wanted to, to keep it as stock as possible. But rather be safe. Lucky I found a steel fork with tabs nearly identical to the stock one. Only difference is 395 ATC instead of 400 and 1 1/8 ahead steerer tube instead of 1 1/8 threaded. Needed a new headset and purchased a wolftooth silver. Kinda messed up and should have ordered the pewter (high-polish) but they're out of stock anyway.

NeedARealBike

Nice. I remember seeing this bike on that neckbeard site. Readit.

pressed001

Been considering groupset options. Was impressed by the Campagnolo Ekar group and its range. Would work well with this 26" build and a 44t chainring.



However, the gear-steps are big and I most likely could not use a 44t ovalized chainring whilst maintaining a good chainline.

Here's a Kapic crank with 40T chainring, no DS spacers:







Considering the range, gear-steps, chainrings and chainline, I've decided to stay with a modified Shimano 2x11 group using a Rotor Kapic MTB crank with ovalized 50/34 chainrings, Ultegra R-8000-GS RD, and a 3T Bailout 9-32 cassette.

pressed001

I have been in contact with White Industries about the hubs. Just FYI; they do offer the Campagnolo N3W freehub but only for their CLD hubs. For the 3T cassette, I will need the SRAM XD or XDR driver.

So after much deliberation I am relieved that the research is finished and the building can soon begin. Lead-time on the hubs is at least 5 weeks. I'm thinking 8 but we'll see.

Moisture

I dont think I've ever seen a cassette with a 9t gear before. I would much prefer a 13t cassette. I feel like I can go faster with 12t down a steep gear than 11t.

So what's your decision re tire size?

If you want to use thin tires, you can try out a 650bx1.5 wheelset. The overall diameter would be identical to using 26x2.

pressed001

Interesting point. I could not find anything stating increased mechanical friction from small cogs. Here's a good article.

Starting out with chosen 35x559 tire and will go from there. Looking forward to the build.

Moisture

Not so much about mechanical friction, but sort of like achieving an optimal balance between top speed and average cadence in accordance to the majority of hills you may encounter in your area.

I feel like a 12 or even 13t cog can help me spin faster down most hills.

Wildwood 

Are you tracking the cost of this build?
Love to see that at the end.

HTupolev

There's a tiny bit. On the order of maybe a watt when dealing with drivetrains that go as small as 11T versus a classic 14T; obviously it gets worse when you go smaller, but it's not huge.

https://www.ceramicspeed.com/media/3...ize-report.pdf

Smaller cogs force the chain to bend and unbend to a larger degree when it engages and disengages with the sprocket.
Also, the way that the chain engages with cogs is more like if they were polygons than circles; as the tooth count decreases, the cog does a worse job of approximating a circle. This is why the 11T cog tends to "feel rough" compared with the 12T or 13T cog next to it, even when the chainline is good and nothing is interfering or rubbing with anything.

Smaller cogs can wear substantially faster, since they don't distribute load over as many teeth.

Drivetrains that use super-small cogs generally do so in conjunction with smaller chainrings than would otherwise be employed. Even with 35mm tires on 26er wheels, 50-9 is a huge gear ratio, about 138 gear inches. For comparison, professional racers usually set up their road bikes with top gears in the range of 120 to 132 gear inches.

Moisture

HTupolev is this why I feel like I can go faster on a 12 or even 13t final gear?