Top Speeds...ooo errr

[blackshiver]

I have a standard four speed 20DC which when thrashed struggles its way to about 50 and a needles width.
I don't have the option of replying to the question "How fast does it go?" with the retort "How fast do you want it to go son".
Is this normal - and how fast is Your Greeves (any, standard or tweaked).

[John Wakefield]

20DC top speed

The 9E was never a high perfomance engine in standard form but I would have though it should be good for 65mph under favorable conditions. Have you checked you speedo, maybe its reading a bit slow. Get someone to follow you in a car.

[blackshiver]

20 DC Top Speed

If I put the Nametab engine from my MDS into the 20DC will I need a new speedo or will it still read slow?
Come on Gentlemen (and Ladies) who's got any Greeves that goes quicker than 50mph. No porkies now, at least I was honest.

[Stuart Baskill]

I have a standard four speed 20DC which when thrashed struggles its way to about 50 and a needles width.
I don't have the option of replying to the question "How fast does it go?" with the retort "How fast do you want it to go son".
Is this normal - and how fast is Your Greeves (any, standard or tweaked).

In 1965 I remember hitting 53mph uphill in 3rd with my 9E Excelsior.Why that figure has stuck in my mind I dont know..I dont remember any level speeds as Sheffield is all hills. Downhill it used to run away with itself.I was only 2/3 of my present size then!!!! Perhaps thats why on my way to work one morning after a 3 mile downhill run there was a load bang.Fortunately the engine stalled as for some reason I took off my glove and felt under the engine.The main shaft nut had escaped and I put my fingers on a very hot primary chain !!!!!!

[John Wakefield]

9E top speed

Back in 1956 Motor Cycling road tested a 197cc (9E) Panther & got 61 mph in top & 53 mph in third.

[Colin Sparrow]

Come on Gentlemen (and Ladies) who's got any Greeves that goes quicker than 50mph. No porkies now, at least I was honest.

My 32DC Sports Twin (325cc Villiers 3T engine) will pass 70mph on the flat.

My 24RCS Silverstone would do 110mph on Snetterton gearing. (Calculated from rev-counter reading on the Hanger Straight). And it would keep up with the Ducatis down there.

My short-stroke MX4 Challenger-engined 250 sprint special was recorded at 90mph at the end of a standing-start quarter mile. Doing 6000rpm. It would usually do the quarter in the low sixteen seconds. Got the data sheets to prove it!

Fast enough for you?

[dave higgins]

Not bad colin, but would it out pace my 49cc villiers lawn mower, its an 8 port, single under head gasket, turning a four inch rotary blade!!.
Set up for a two inch cut over twenty five yards, it can reach speeds of 5 & quarter mph, ( calculated by my sundial ) on the washing line straight...., dave.

[pgc40]

So I took my 1965 Challenger mx 2 out today for a test run and it happily ran at 41.9 mph on the road in 4th (top) gear although at a push it would probably do 50 mph. My Smiths speedometer is surprisingly accurate as I thought I would use DigiHUD speedometer app on my mobile phone which you can download for free see http://digihud.co.uk/blog/
My ISDT challenger has a wide ratio Albion gearbox and seems to geared well for green laning (acceleration and climbing hills is good) and a little bit of roadwork. I once tried a smaller rear sprocket for the Beamish Trophy Trial and it struggled to get up the hills but could do 55 mph on the flat

[John Wakefield]

This highlights the problem of the 4 speed gearbox, a five speed gives a much higher top gear with acceptable gaps between the lower gears. With the power available from an MX2 it should give over 70mph in top with suitable gearing, but of course (as you have stated) at the expense of first being too high This makes the Greeves uncompetative in ISDT type events that entail road sections. Even with a 500 Yamaha that I rode in the Welsh 2 Day back in the 1970's a 5 speed box was essential.

[tony]

The GBA box gearing is really good on the 250 and great with the extra power of the 380. It certainly rips up muddy hills (no sand here) and according to the sheet will do 90mph in top - not that I would fancy that.

My bike has the correct 15T engine sprocket and correct GBA box - has the makes you smile factor

[John Wakefield]

Is this the spec for the 250 or 380? Iwould think 90 mph for a 250 (or even the 380) in enduro trim would be a bit optomistic, presumably the MX4 that Colin sprinted had close ratio gears, clip on bars, rear sets, and road race tyres
It is interesting to compare the gear ratios with the 1977 Suzuki PE250 a popular enduro of the period. http://www.yeoldecycleshoppe.com/roa...e250-road-test
Gear ratios for the PE (a 5 speed box) are:
1st 27.96
2nd 18.356
3rd 13.11
4th 9,57
5th 7,26
Even with a 5 speed box the tester remarked that in certain conditions the rider can be stuck between gears because the engine wont quite jump the ratio span to the higher gear without bogging. With regards top speed the tester states that it has enough power & gearing to sustain a speed of 70mph for long periods

[tony]

380 specification

[John Wakefield]

On the gearing specified the engine would be reving at around 9000 rpm at 90 mph

[dave higgins]

You would need the amount of teeth on the chain wheel to calculate the engine rpm!
as far as I can see from my phone it does not give that info.

[John Wakefield]

Dave I worked it out comparing it with the PE Suzuki. Both would have an 18" back wheel the PE has a 450 x 18 tyre the Greeves would probably had a 400 x18 so slightly lower gearing
Overall top gear ratios are 7.26 to 1 on the Suzuki and 6.91 to 1 on the Greeves. The MPH per 1000 rpm on Suzuki is 10.7 mph so calculating the higher ratio of the Greeves at 10.1 mph per 1000 rpm would then make around 9000 rpm at 90 mph. Given that both bikes had same size back wheel the relationship of rpm to mph is related to the gearing factor and would be the same irrespective of bikes.