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SUBLIM8er
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2,209 Posts
Discussion Starter · #1 ·
Question: What is the shortest TT length one could safely run with a 17.5 inch frame? Is 23.8 inches too long? Do top tube lengths generally run longer on 29ers than 26ers to achieve toe clearance from the front tire? Your responses will help me with my final frame measurements.
Thanks!
 

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SUBLIM8er
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2,209 Posts
Discussion Starter · #3 ·
Here you go:
HT angle=72
ST angle=72
BB height= 12.01 inches
fork rake= 45
crank length=175
shoe size = 45
 

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Recovering couch patato
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13,971 Posts
what you're asking is going to cost even the best designer at least 15mins to figure out,e ven if you provide perfect specs about the toe clearance you'll need. Try and measure BB center - tip of toe. That plus the wheel radius will be your minimum front center I guess.
 

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Student of the Bike
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821 Posts
Axis II said:
Here you go:
HT angle=72
ST angle=72
BB height= 12.01 inches
fork rake= 45
crank length=175
shoe size = 45
Interestingly enough those are almost my exact numbers for my custom WW that Walt began this week. The only difference is that my fork rake is 39 (Reba) and shoe size is 44. In order to come up with the right toe clearance we went with a 23.9 TT, which gave me a 7 toe clearance.

I just plugged in your numbers into my spreadsheet and it gave you 8mm of toe clearance. Looks like you'll be OK but I'd definitely run this past a builder before you lock down anything.
 

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SUBLIM8er
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2,209 Posts
Discussion Starter · #8 ·
CBaron said:
Interestingly enough those are almost my exact numbers for my custom WW that Walt began this week. The only difference is that my fork rake is 39 (Reba) and shoe size is 44. In order to come up with the right toe clearance we went with a 23.9 TT, which gave me a 7 toe clearance.

I just plugged in your numbers into my spreadsheet and it gave you 8mm of toe clearance. Looks like you'll be OK but I'd definitely run this past a builder before you lock down anything.
Small world. I'm wondering/rethinking my choice of the relatively slack 72 ST angle. What do you think? How did you come up with your ST angle?
 

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Student of the Bike
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821 Posts
Axis II said:
Small world. I'm wondering/rethinking my choice of the relatively slack 72 ST angle. What do you think? How did you come up with your ST angle?
My focus was going for as short a wheelbase as possible(42 or less) and Walt's direction was on my front center number (635). We started with a 73 STA, but due to some of my passed bikes geometry numbers, changed to a 72 STA and then lengthened the TT by about 1/2". A greater STA will eleviate some issues like toe overlap but it will also increase front center and wheelbase unless you shorten the TT.

I'm 5'10" with about a 33" inseam. Walt said that this bike is as "tight" of a frame that could be done for me w/o creating issues. I must say that I've learned quite a bit through this process.
 

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Premium Member
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48,161 Posts
CBaron said:
My focus was going for as short a wheelbase as possible(42 or less) and Walt's direction was on my front center number (635). We started with a 73 STA, but due to some of my passed bikes geometry numbers, changed to a 72 STA and then lengthened the TT by about 1/2". A greater STA will eleviate some issues like toe overlap but it will also increase front center and wheelbase unless you shorten the TT.
Think about this for a moment.

If the headtube angle, fork rake and TT length remain the same the front center will get longer with a steeper seattube angle and shorter with a slacker STA.

If the HTA, fork rake and front center do not change the TT length will be shorter with a steeper STA and longer with a slacker STA.

None of these frame numbers mean much by themselves. They have to work as a whole. It sounds like Walt is doing it the correct way - setting the important points; position over the BB, the needed toe clearance, reach to the bars. After that the numbers are whatever they end up being even if they may not look "normal".
 

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Student of the Bike
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821 Posts
Sure but...

The numbers weren't set. I was wanting some of the numbers to change (based off passed bike's geometry). I.e. I was wanting to get a little further back over the bottom bracket and was willing (wanted) to go with a little longer TT. It worked out well because that was needed to give the proper toe clearance.

Of course all the numbers work as a whole but bikes can be given certain personalities by adjusting variables outside of reach, position v BB and toe clearance. I generally gave Walt what I wanted in a "bike personality" and he took care of the things that needed attention.
 

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Premium Member
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CBaron said:
The numbers weren't set. I was wanting some of the numbers to change (based off passed bike's geometry). I.e. I was wanting to get a little further back over the bottom bracket and was willing (wanted) to go with a little longer TT. It worked out well because that was needed to give the proper toe clearance.

Of course all the numbers work as a whole but bikes can be given certain personalities by adjusting variables outside of reach, position v BB and toe clearance. I generally gave Walt what I wanted in a "bike personality" and he took care of the things that needed attention.
I still do not think you really understand what I am saying.
With the slacker STA the TT has to be longer to keep the same front center.
An offset seatpost could have given the frame an effectively slacker STA and an effectively longer TT.
Either way the overall fit does not really change.

It is obvious that Walt knows what he is doing, though.
 
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