pressed001

Hello,
Looking at the geometry and how all this would work out. I decided to throw my road wheels on, and what do you know, it fits great.


I will do a disc conversion in some manner. I will pull it off even if I have to get an IS mount welded to the fork and some kind of adapter installed on the rear. Getting an original 395 ATC fork is impossible. Origin8 has one with a threadless 1 1/8 steerer tube which looks good, but I'd still have to get it stripped, polished and chromed again. So the extra costs will be about the same as staying with the original that I have.

I'm having trouble deciding between whether to go 26" road bike or 700c road bike. I will build the wheels up myself which will be either 559x35 or 622x35 both wearing some 1.35" (35mm) slicks (Kojak's). The rims will be tubeless and hookless regardless of BSD. For the 622 variant, I'll be using some 30mm deep XC mountain rims. Anyway, there's enough clearance for the 1.35" tires for the 700c setup.

What I'm wondering is if the 31cm BB height with the 700c set-up will be just too much. The 26" setup will be 6.3cm lower which would give a more aggressive road bike. Also to consider is the really long wheelbase which I think is about 1200mm. (20" 1995 GT Tempest)

I don't care about the wheel-size, but I want an aggressive road bike in the end, which I think leads me towards 26" wheels. The 700c looks better, but the higher COG will be a compromise.

Here's a pic of the original build:


Thanks for your input.

shelbyfv

Cool looking bike. Get some nice 26" slicks https://www.renehersecycles.com/prod...tires/26-inch/ and do a drop bar conversion. There is lots of inspiration in C&V https://www.bikeforums.net/classic-v...nversions.html

msu2001la

This looks like a cool project. I'm curious about the "disc conversion" aspect. I was always under the impression that even if you could weld mounts onto a frame to accommodate discs, that because the frame wasn't designed to withstand brake force at those points, it was a bad idea? Just wondering if this holds true, or if you've done anything else to this frame/fork to make it work differently with discs?

As for wheel size, I'd definitely agree that 700c is a better choice if your end goal is to make this into an "aggressive road bike". The BB is going to be very high though.

70sSanO

Aggressive road bike? Even with a 90’s mtb, I can’t imagine a HA over 71 degrees, before the larger wheels; less after.

You can make it a drop bar, but I doubt the handling will be close to a road bike.

John

HTupolev

Modifying your existing fork will also destroy the finish.

No it won't.

You may be able to achieve fairly close performance to a road bike. But if you want it to feel like an "aggressive road bike", I'd recommend starting from a road frame.

pressed001

Thanks for the links. Definitely seen some cool bikes there. But no disc or 700c conversions, so I am maybe encroaching on some more rare ground with this project.

Well with these 90's GT Triple Triangle frames, there are a lot of ppl that have converted the rear brake with a simple brake adapter which you can see here. From what I hear, the rear drop out and seat-stays are girthy enough to handle the extra force. The front brake exerts more force onto the fork, so it is suggested to get a disc specific fork or to reinforce the fork with some added steel. This is also typically done for the rear brake conversions, but this frame is aluminum, so any after-market welding is a no-go. I looked extensively into that topic and what I heard from bike builders is that the aluminum warps slightly from the welding so you'd need to set it somehow to keep it in its stock form. After that you'd also have to heat treat the aluminum again. The bike builder with whom which I spoke, said that this kind of stuff can basically only be done by the original manufacturer. Heat treating can be done by anyone, but keeping the frame from warping, or setting it was the hard part as far as I understood.

shelbyfv

I'd forget the discs if you hope for a fast bike. The frame and fork reinforcement needed plus the extra weight of the brakes will add a few pounds. Frankly I don't see a point in messing up a nice vintage MTB frame when there are plenty of road frames available.

pressed001

I had it finished, and will so do it again!


559-622= -63
Ahh, now I see...
-63/2=-3.15cm
Thanks.

If I did that, it wouldn't be nearly as fun, or special. I love this frame. It needs to be disc though and I built a carbon rigid last year as a replacement. Speaking of which, if I stick to 559 rims, I can always go back to a mountain setup without having to invest in new rims. Even more reason to stick with the 26" setup.

pressed001

I believe the HA was 71.5 on this one. Correct me if I'm wrong. Can't look it up as the documentation is on my other computer. So long both wheels are same diameter and fork ATC remains stock, HA does not change from stock.$

You could very well be right. Lots of ppl convert these old GT's though. I guess we'll find out.

pressed001

Well discs will allow me to run much better wheels and tires. There will be some added weight, but nothing extreme and I don't think reinforcement of the seat-stay will be required. Will find out one way or another, right!

I will also be removing the old v-brake bosses and re-polishing those areas. Should really help to clean the frame up. I know that any die-hard classic fan will recoil at the thought, but yeah, v-brakes just aren't my thing, even on my road bike (or caliper rather).

HTupolev

How will it allow you to run better tires?

I'm confused at how the pieces of this build fit together. Like you're telling us that you're going to use tubeless hookless rims and fancy tires, but also say that you're running Kojaks, which are a fairly basic non-tubeless tire.

70sSanO

Yes. So used to front suspension changes I forgot the same front and back.

Good luck with it. I won’t be trading in my Cannondale Criterium for one.

John

msu2001la

Ah, cool. I hadn't seen those adapters before. Looks like they require drilling mounting points on the the dropout which sounds a little terrifying to me, but they do appear to work.
It's an awesome frame, good luck with the project. I'd love to see photos when it's done.

pressed001

Well you're right in a way, I guess the tire isn't better. However, on a 30mm inner width rim, the pressure can be substantially reduced increasing comfort. Grip and rolling resistance will also get a boost by the contact patch shape change. This is really more for road bikes, where wider tires give a round contact patch instead of a long skinny one (skinny tires). There's a few advantages to running wider slicks on road bikes. I am pushing the envelope with the 35mm. I think current market is at 31mm which is most likely best. But that's also for 700c tires. Really curious to see how this ends up with the 559's.

Any tire can be used as tubeless with tubeless sealant.

Germany_chris

He's talking about their tires

HTupolev

I'm not criticizing your width choice. I totally get wide slicks, including on a 26er drop-bar conversion. Here's my gravel bike, built from an old Stumpy, featuring some 2.1" slicks:



Two days ago I rode 100 miles on it, mostly paved.

No. You might be able to get any tire to seat and seal, but this doesn't make it a good idea. Hooked rims provide safety margin against blow-offs. Inner tubes also provide safety margin against blow-offs.

Because mountain bike tires are often very stiff, and because they're typically used tubelessly at extremely low pressures, "ghetto tubeless" setups on MTBs historically often worked out okay. But it was always sketchy, and road tires are a completely different game. A big part of why tubeless has seen slow adoption on road bikes is that the higher riding pressures combined with the suppleness of the tires means that there is a lot less safety margin to work with. Rims and tires need to be manufactured with much better precision, and the tires need very stiff beads that experience minimal elongation over their service life, so that they consistently form an exact snug fit on the rim's bead shoulder and cannot crawl anywhere.

Putting a non-tubeless road tire tubelessly on a hookless rim is an extremely bad idea.

pressed001

Great points and beautiful photo.

Depends on bead material which in this case is Kevlar. All good points though and will have to pay close attention. Also tire pressure will most likely be at minimum spec @ 55 psi.

Currently running my padrones at 63 on hookless but they have carbon bead. Ran some schwalbe thunder Burt's and also winter spike tires (schwalbe) on hookless no problem. Road hookless is like you say, another animal. Especially with what kind of riding I do.

Will have to keep a close eye and change plans if necessary. Not many 26" slicks out there.

ofajen

Yeah, the geometry is just not very cooperative. I rode a late 80s RockHopper with drop bars for several years, but last year I switched it to swept back touring bars, and I regard that as pretty much settled. Might try something like Jones bars at some point but not going back to drops on this one.

The drop bars, even at 45cm, weren’t even close to wide enough and the handling was very sluggish compared to a road bike. Plus the brakes are much happier with MTB style levers.

Also, I’m developing a fondness for riding that bike in rather messy conditions, and wide bars with close grips are better so I can stay up and keep weight back.

Otto

mstateglfr 

Interesting conversion. Goofy high bottom bracket with 700c wheels, but you clearly know all the negatives going into the project so have a blast and enjoy the experience of tying something different.

Moisture

Interesting enough, I've done something similar with a GT ZASKAR LE frame. I had a front rigid for with v brake for 700c rims so I tried out a basic 700x38 wheekset I had laying around. This frame is not designed for 700c wheels. You'll be best off sticking to 26" rims regardless what you intend doing.

I measured the bottom bracket height at roughly 285 with regular 26" trail tires. Using 700c wheels would raise the bb height by another cm or so. Unless you plan to use very long very cranks, you don't need such a high height for road use.

All in all, it would make a decent urban/road machine, but i would use the rim diameter which the frame was designed for.

HTupolev

That wouldn't be similar at all. Having a 700c wheel just in front would change the geometry far more than front-and-rear, since you'd be slackening the bike's angles. And differences in the fork geometry would alter the situation as well.

Trakhak

Agreed. People planning such conversions often give short shrift to the single most significant indicator of how the converted bike will ride: the wheelbase. Swap out all the parts you want---you'll still end up with the antithesis of aggressiveness. Think 1960s Vistacruiser station wagon wallowing down the road.

70sSanO

There are worse things.


John

Moisture

Yes I understand. But at one point I tried out both 700c wheels front and rear. This is what I was referring to.

Even though the height was balanced fore and aft, I still preferred having even one 26" rim, whether it was on the front or rear. Still better than having two wheels of the wrong size.

shelbyfv

Not to mention no brakes....