Speed

[spike123]

Hi guys
My a65t 1971 when cruising at4000rpm is doing 50mph is this normal as it seems to be revving a bit too much
Is this standard or do I need to up my eng sprocket

[DAVE BRADY]

Hi,

Do you know how many teeth on the gear box sprocket as it is this that would need to be changed.
20T is fairly standard but I run 21T on my A65 and it takes the edge of the busyness of the engine but has almost no affect on slower running.

Dave.

[limeyrob]

It should be geared for about 110 in top at 7000-7500 revs so you can work back from that.   is it a US export model, they were low geared.

[V500]

The only work-back from 110mph at 7500 revs would be retrieve the bits of engine scattered over the landscape..

[redmelons]

Estimated top speed per gear (standard A65, 20/47 final drive) at ~6,200 rpm

Gear   Gear ratio   Estimated top speed
1st    11.49:1   39 mph
2nd     7.32:1   61 mph
3rd     5.24:1   85 mph
4th       4.58:1   97 mph

Notes: calculations use published A65 gearbox ratios and typical 20/47 sprocket final drive and assume ~6,200 rpm as a practical maximum before heavy vibration; actual speeds vary with tyre circumference, sprocket changes, engine tune and redline.

[limeyrob]

Perhaps that's why my frame cracked and the oil once boiled.....

[spike123]

Ok thanks
I dont think it's import

[limeyrob]

It could have been an export model that never got exported.  In 71 and 72 BSA were in real trouble and selling these bike to dealers like Commerfords in big batches in a desperate attempt to ward off bankruptcy.

[scifi]

You say it is an A65T, does the T mean it is the Trials version..?  In which case the speeds are always lower.   I have the same low gearing on my B40 trials bike... Ideal for green-lanes, but useless on the Bypass.
A quick search on Ebay shows that for £30 you can get 16 tooth to 21 tooth gearbox sprockets.   The 19T and 20T being suitable for road use.

[JulianS]

T for Thunderbolt the single carb model not trials.

[V500]

A thunderbolt trials version would be mind-boggling..

[nablats]

I just got my 62 tbolt on the road, tried a 19t front as there are many 1in3 hills around these parts (north york moors). After just a couple of runs I went to 20t as it has plenty of grunt (I am new to these 650s) when I changed the oil seal behind the sprocket (the only blumin seal I didn`t change). I will get a 21t to try once I get some miles under my belt.