Britbike forum Forums British Motorcycle specific Brands Triumph bulletin board Top speed Bonneville

A friend was over at my house today. He has a 1979 750cc Bonneville, and we where discussing it`s top speed. I suppose this is the best place to get a good answer..

He claims the bike has done about 110mph, does this sound about right ??

right after he went over a cliff

Was this acording to HIS speedo??
not saying the bike can, or can not do it...but just that often, the speedo`s cant be trusted...

Don't even think about believing a 35+ year old Smiths instrument. Seems there was always bit of difference between Smiths mph and "real" mph anyway. Am I the only one to notice that the machines that were advertised as 120mph roadsters never quite seem to find a verifiable "ton" on the salt? I've seen a lot of 115+ mph bikes check out at 95-96 mph on a gps or properly adjusted $25 bicycle speed-o.
Don R.

Top speed on a 79 should be about 105-107 mph. The tests at the time estimate around 107, but the tester probably weighed 150 pounds. A note on top speed runs at Bonneville. The salt slows down a bike by 10-15 mph. There just is not the same grip as asphalt and there is much more friction on the tires. Why not just take it out on the freeway and find out? Just don't rev it over 7k. I have done 90 on my 79 and it was still pulling. I'm sure the speedo is off a little but not by more than 10 mph.
Scott

if 107 was the test speed, and his is good and he doesnt weigh 300lbs ABOUT 110 is reasonable...how long to do take your eyes off the road to see is that 107 or 110 flickering about there..we'll allow him the benefit of the doubt

Weight factors into the equation for acceleration, but not for top speed. A 300 pound guy would have a lower top speed only because he was less streamlined.

to a degree..there must be a point where weight would require a 10 mile straight to get there or regearing as it'd never reach peak revs in top

110 is a highly doubtful on a stock '79 T-140.

But given the right cams, headwork, carburation, exhaust, gearing, etc....

649, yes, that is true. If you load on enough lard, you may never find a road long enough to accelerate to top speed - at least on an old Bonnie. But given a powerful enough bike, say a GSXR1000, a 300lb rider and a 150lb rider would both be able to get to the same top speed so long as the 300lb guy could still tuck behind the fairing.

rossi can go on a pasta binge then!!!!

"110 is a highly doubtful on a stock '79 T-140."

VA Rebel,
110 mph is not doubtful at all on a 1979 T140E. In Cycle World's test of the 1981 T140ES the top speed was listed as 112.

I think this thread exposes a larger issue. The T140 is a good machine. Just as exciting as the T120. The Bonneville didn't change as much as the motorcycle industry changed. A 13.8 quarter mile was lightning quick in 1968 but in 1978 a fast quarter was below 12 seconds.
Scott

Scott, I like the T-140, otherwise I wouldn't own one. But, I don't take magazine articles for the gospel either.

If you have a stock T-140 that will do a honest 110 mph (not as indicated by Smiths or Veglia) you've got a mighty good one.

A modified T-140 is a different story.

I once did a speed day with Performance Bikes magazine at Bruntingthorpe airfield. There were 4 of us on Triumph based bikes, results were as follows:
Standard (but well used) T140 105 mph
Morgo 750 Triton (me) 117 mph
750 TSS Triton 119 mph
920 Weslake Triton 132 mph.

I would think 110 would be easy out of a reasonably well sorted T140.

I'm going to a Top Speed event at Elvington airfield this weekend on the 850 Weslake which I've now overgeared specially. Last time on a similar spec Triton I managed 134 mph. Going for something similar on Sunday trying to better 126 mph from last time out.

Cheers

Bob