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Why is it that the standards for thru bolts are beefier on the front wheel vs the back wheel (20mm vs 12mm)? Doesn't the rear wheel deal with higher forces?
 

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Disc brakes place a lot of torque on wheels. 75-80% of braking forces is on the front, plus the front hits the rock garden first. The rear just follows.....if everybody went back to v-brakes, thru axles/bolts would not be necessary.
 

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I always thought rear axle size was limited because you have to wrap a cassette/lockring round it and getting every manufacturer to agree to a new standard is one of those great impossible things. So hub/frame designers stuck with improving what they had.

Before through axles the rear one was always beefier (9mm front, 10mm rear).
 

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suspension forks have bad mechanics for keeping the wheel lined up with the fork. The rear triangle has a lot better shape to make rigid. The through axle front fork works as a significant part of making the fork rigid. The forks lowers, crown and axle make a rectangle. It is difficult to make that shape stable.
 

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Fix the Spade said:
I always thought rear axle size was limited because you have to wrap a cassette/lockring round it and getting every manufacturer to agree to a new standard is one of those great impossible things. So hub/frame designers stuck with improving what they had.

Before through axles the rear one was always beefier (9mm front, 10mm rear).
Not so much the cassette lockring, but the freehub body ratcheting mechanism.

To use a larger diameter rear through axle the FH would need to be increased in diameter to remain reliable with would require a new cassette with a larger inside diameter and then the smallest possible cog would be much larger than the current 11T, which would require larger chainring to keep the gearing range...
 

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AlliKat said:
suspension forks have bad mechanics for keeping the wheel lined up with the fork. The rear triangle has a lot better shape to make rigid. The through axle front fork works as a significant part of making the fork rigid. The forks lowers, crown and axle make a rectangle. It is difficult to make that shape stable.
Certainly there are limitations to the standardized freehub/cassette, but the advantages gained by a 15-20mm TA up front are far greater than even a 12mm TA on a rear triangle. Most frames have a rear end that is far more stable and rigid in terms of twist/flex with a similar sized axle in place when compared to a suspension fork.
 

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shiggy said:
To use a larger diameter rear through axle the FH would need to be increased in diameter to remain reliable with would require a new cassette with a larger inside diameter and then the smallest possible cog would be much larger than the current 11T, which would require larger chainring to keep the gearing range...
that would be ok with me...please get on that Shiggy. thanks in advance
 

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dullertap said:
Why is it that the standards for thru bolts are beefier on the front wheel vs the back wheel (20mm vs 12mm)? Doesn't the rear wheel deal with higher forces?
20mm rear ends have come and gone. There was not a discernible advantage over the 12mm. Razor Rock was about the only one who produced a true 20mm thru axle hub though, most others were smaller 12-15mm axles with adapters to 20mm.
 
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