Rev counter/speedo - which do I believe?
Discussion
Hi all - I'm a PH newbie but Chim owner of 3 years. Can any of you advise me on the following please?
My Chim has never seemed to enjoy being driven at higher speeds. When the speedo gets above 90 everything seems to shake and rattle a bit, and not in a wheel balance type of way either. Door mirrors visibly shake, as does the bonnet, and the whole thing feels like its on the limit. The easy solution seemed to stay below 90 - not a problem on most of my journeys plus giving the added benefit of keeping my licence (it balanced precariously on 9 points until recently!). However, today I thought I'd go for a bit of a blast in the sunshine before garaging the car for a while, and I started wondering about the speedo vs. rev counter readings. My Chim seems to pull quite smoothly all the way to about 6700 ish revs, and on a nice empty bit of road (private one, naturally!) I floored it through the gears until I was doing 110 according to the speedo, in 5th gear. At this point the rev counter was showing 5500 rpm. This started me wondering... with only 1000 rpm or so left, how could the car reach its theoretical maximum of 160+ mph? I got home and started researching, only to get even more confused - I found an old topic on here which gave loads of complicated calculations, which seemed to suggest that at 5500 rpm in 5th, I should have been travelling at 159mph!!! Was I??? It would explain all the shaking mirrors etc., but I can't believe I was going that fast. Could the rev counter be that far out? Or have I misunderstood the calculation (maths - "..could do better"..) Or might I have a strange diff fitted? Would appreciate any ideas. Car is an early 4.3 Chim by the way.
My Chim has never seemed to enjoy being driven at higher speeds. When the speedo gets above 90 everything seems to shake and rattle a bit, and not in a wheel balance type of way either. Door mirrors visibly shake, as does the bonnet, and the whole thing feels like its on the limit. The easy solution seemed to stay below 90 - not a problem on most of my journeys plus giving the added benefit of keeping my licence (it balanced precariously on 9 points until recently!). However, today I thought I'd go for a bit of a blast in the sunshine before garaging the car for a while, and I started wondering about the speedo vs. rev counter readings. My Chim seems to pull quite smoothly all the way to about 6700 ish revs, and on a nice empty bit of road (private one, naturally!) I floored it through the gears until I was doing 110 according to the speedo, in 5th gear. At this point the rev counter was showing 5500 rpm. This started me wondering... with only 1000 rpm or so left, how could the car reach its theoretical maximum of 160+ mph? I got home and started researching, only to get even more confused - I found an old topic on here which gave loads of complicated calculations, which seemed to suggest that at 5500 rpm in 5th, I should have been travelling at 159mph!!! Was I??? It would explain all the shaking mirrors etc., but I can't believe I was going that fast. Could the rev counter be that far out? Or have I misunderstood the calculation (maths - "..could do better"..) Or might I have a strange diff fitted? Would appreciate any ideas. Car is an early 4.3 Chim by the way.
My speedo is way out at higher speeds, although it over reads. For me I compare the mph readout on my trusty little 'tomtom one' which being satnav is pretty accurate. As for under reading, it may very well do that but usually they over read as far as I'm aware.
It's a bit extreme to buy a satnav for accurate speedo, but they are marvellous bits of kit
Funny, but my chim is a little shaky at 70 but really smooths out the faster it goes after that....
Odd one ... the rev counters are usually pretty accurate. But I'd be surprised if an early 4.3 would pull 159mph, or your speedo be low.
However, it is not unusual on these cars for things to start wobbling at speed (by that I mean 140+). My Griff 500 bonnet used to start flexing a bit at 140-150 due I guess to the amount of air swirling around the engine compartment.
I suggest using someone with sat nav to do some runs with and do checks at various speeds.
However, it is not unusual on these cars for things to start wobbling at speed (by that I mean 140+). My Griff 500 bonnet used to start flexing a bit at 140-150 due I guess to the amount of air swirling around the engine compartment.
I suggest using someone with sat nav to do some runs with and do checks at various speeds.
Not sure if its the same with chimaeras and griffs, but I had a bad shake on my griff at about 85.
Took it in to get ALL the wheels balanced, the rears were quite badly in need of balancing.
This made alot of difference.
Also do the chimaeras have front spoilers?
My griff didnt have one, so I bought one from Ian @ Sportmotive, and its made alot of difference. Quite smooth even at 125 (on private road , you understand)
Oh and the tacho thought, on a GKN diff of 3.31:1 and a rover box, its 28.3mph per 1k on the tacho, in fifth.
Took it in to get ALL the wheels balanced, the rears were quite badly in need of balancing.
This made alot of difference.
Also do the chimaeras have front spoilers?
My griff didnt have one, so I bought one from Ian @ Sportmotive, and its made alot of difference. Quite smooth even at 125 (on private road , you understand)
Oh and the tacho thought, on a GKN diff of 3.31:1 and a rover box, its 28.3mph per 1k on the tacho, in fifth.
Edited by antonyj on Saturday 16th December 23:14
burriana said:
Odd one ... the rev counters are usually pretty accurate. But I'd be surprised if an early 4.3 would pull 159mph, or your speedo be low.
However, it is not unusual on these cars for things to start wobbling at speed (by that I mean 140+). My Griff 500 bonnet used to start flexing a bit at 140-150 due I guess to the amount of air swirling around the engine compartment.
I suggest using someone with sat nav to do some runs with and do checks at various speeds.
However, it is not unusual on these cars for things to start wobbling at speed (by that I mean 140+). My Griff 500 bonnet used to start flexing a bit at 140-150 due I guess to the amount of air swirling around the engine compartment.
I suggest using someone with sat nav to do some runs with and do checks at various speeds.
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