On May 18,1977, appellant and a co-defendant approached the victim, who was riding his bicycle on a public street in Philadelphia, and knocked him off of the bicycle. The co-defendant then chased the victim a short distance with a *585knife, meanwhile directing appellant to take the bicycle. The victim, in fear of the knife, ran in one direction, and appellant and his co-defendant ran in another. They were apprehended shortly thereafter. Appellant was convicted of robbery,1 criminal conspiracy,2 aggravated assault,3 and possession of an instrument of crime generally.4
Appellant’s argument that conviction of both criminal conspiracy and possession of an instrument of crime generally is prohibited by the Pennsylvania Crimes Code5 has not been preserved for appellate review because of the appellant’s failure to raise the issue in specific written post-trial motions. Commonwealth v. Blair, 460 Pa. 31, 331 A.2d 213 (1975); Commonwealth v. Gadson, 234 Pa.Super. 648, 652, 341 A.2d 189, 192 (1975).
The judgment of sentence on the conviction of aggravated assault, however, must be vacated. The issue is not one of merger of this offense into the crime of robbery, as appellant contends, but rather, whether the facts of this case come precisely within the Crimes Code definition of robbery.6 The evidence is insufficient to support convictions for both offenses, because it does not show that the pursuit of the victim by appellant’s knife-wielding co-conspirator had any purpose outside of “the course of committing [the] theft” for which appellant was tried and convicted.
The cause need not be remanded for resentencing. Appellant was sentenced to eleven and one-half of twenty-three months’ imprisonment on the aggravated assault and *586robbery convictions, and to five years’ probation on each of the other two, the four sentences to run concurrently. Aggravated assault, under the subsection of the Crimes Code on which sentence was imposed, is a misdemeanor of the first degree7 while robbery is a felony of the first degree.8 It is thus clear that sentencing on the invalid conviction did not influence sentencing on the other counts prosecuted simultaneously. See Commonwealth v. Senyszyn, 266 Pa.Super. 480, 405 A.2d 535 (1979); Commonwealth v. Fant, Pa.Super., 398 A.2d 704 (1979).
Judgment of sentence on Information No. 695 vacated; Judgments of sentence on Informations No. 693, No. 694 and No. 696 affirmed.
WIEAND, J., files a dissenting opinion.. 18 Pa.C.S. § 3701(a)(l)(ii).
. 18 Pa.C.S. § 903.
. 18 Pa.C.S. § 2702(a)(4).
. 18 Pa.C.S. § 907(a).
. See 18 Pa.C.S. § 906.
. See 18 Pa.C.S. § 3701(a)(l)(ii).
. 18 Pa.C.S. § 2702(b). The maximum possible sentence is 5 years. 18 Pa.C.S. § 1104(1).
. 18 Pa.C.S. § 3701(b). The maximum possible sentence is 20 years. 18 Pa.C.S. § 1103(1).